Our long-term goal is to provide clinicians with a theoretical framework of mobility and framework-derived measurement tools to improve rehabilitation of persons who have mobility restrictions consequent to a stroke. Recovery of mobility from stroke requires restoration of independent muscle excitation from the mass extension and flexion muscle co-activation commonly observed post-stroke. The basis of the theoretical framework used in this study is to delineate the relationship between lesion damage to ipsi- and contra-lesional corticospinal tract and cortico-recticular pathway and muscle co-excitation impairment and the limitations in the execution of the biomechanical functions needed in mobility (e.g., body support and forward propulsion). In past projects where self-selected walking was studied, healthy persons were found to use a small set (n=4) of independent muscle co-excitation patterns to execute the critical biomechanical functions. Persons after stroke walk slower with suboptimal execution of the biomechanical functions because they cannot activate the patterns independently; instead they merge the patterns. The aim of this project is to assess the limits of mobility capability of healthy and post-stroke persons within this framework by having them perform a variety of tasks fundamental to household and community walking, such as how fast they can initiate or stop walking: speed up or slow down, or turn. Experimental analyses of each task will determine how the number, muscle composition and neural control (timing and magnitude) of the independent muscle co-excitation patterns limit body support, body forward propulsion, body mediolateral control, leg propulsion, foot clearance, and muscle mechanical energy production. Across the different mobility tasks, we expect the merging of the late stance pattern (e.g., plantarflexors) with the early stance pattern (e.g., hip and knee extensors) into a stance pattern will be one primary coordination impairment because their contributions to body support and propulsion then conflict at times or are wrongly timed. Another primary coordination impairment expected is the merging of the swing-to-stance pattern (e.g., hamstrings) into the early stance pattern such that leg deceleration at the end of a step cannot be independently controlled. In future projects the relationships found here delineating how muscle coordination impairment limits biomechanical function execution will be used to create a clinical assessment and decision-making ?toolbox? capable of inferring patient-specific deficits in muscle coordination and biomechanical function execution, and their impact on limiting household and community walking. Thus, clinicians will be able to guide individual treatment and monitor individual rehabilitation progress.